1. Field of the Invention
The present invention relates to improved shift logic for an automated vehicular mechanical transmission system. In particular, the present invention relates to a control method/system having logic rules whereby shifts are commanded only at substantially steady-state throttle conditions to minimize the occurrence of unwanted shifts.
2. Description of the Prior Art
Fully and partially automated vehicular mechanical transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,595,986; 4,648,290; 4,850,236; 5,109,721; 5,393,276; 5,409,432; 5,425,284; 5,761,628 and 5,938,711, the disclosures of which are incorporated herein by reference. Such transmissions having an automatic shift mode typically base shift decisions upon shift point profiles or shift schedules, which often are graphically represented on a graph of throttle position (demand) versus engine, output shaft or vehicle speed. It is known to temporarily modify these shift profiles in view of various sensed vehicle operating conditions to modify vehicle performance, for antihunt purposes or the like. Examples of such shift logic may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,551,802; 4,852,006; 4,916,979; 5,053,963; 5,406,861 and 5,938,711, the disclosures of which are incorporated herein by reference.
A problem not addressed by the prior art shift logic involves unwanted shifting which occasionally occurred due to determining which shifts were required, and commanding initiation of such shifts, when the operator was changing throttle pedal position.
Present demand-based shift point algorithms typically use instantaneous demand to determine the shift point speeds. In cases of steady-state or very slowly varying demand, this provides logical shifting responses to the driver's demands. However, in the case of demand (usually expressed as a throttle pedal position) which is changing relatively quickly, this strategy can create shifts which do not follow with what the driver is trying to do.
In one example (see copending U.S. Ser. No. 09/145,316), if the driver is on the throttle but below the upshift point associated with his particular demand and then comes off the throttle, an upshift can be triggered with the present shift strategy as the demand transitions toward 0%. In this case, the driver may have intended to slow down, but the system upshifted. In another case, if the driver is off the throttle and then gets on it, an upshift can be triggered as demand increases. The driver may have wanted more power, but again, the system upshifted. In both cases, responding to a transitory demand level caused the system to upshift when the situation might have been better handled by remaining in place.
Also, it may be undesirable to determine if a shift is required and/or to initiate shifts during a transient of demand, as the driver may change his mind and/or throttle pedal oscillations may be the result of the vehicle traveling over a rough surface.